1. Field of the Invention
The present invention relates to a tesser type lens system having an aperture stop located at the rear of the lens system and more particularly to a lens system of this type having a relatively wide field angle of about 60.degree. and an F-number of about F. 2.8.
2. Description of the Prior Art
The prior art is quite familiar with various forms of tesser type lens systems having a rear aperture stop. These photographic objectives are frequently used in compact cameras, for example, to facilitate the incorporation of a shutter mechanism into the camera body. Numerous examples of prior art literature exist disclosing a tesser type lens system having an aperture stop located at the rear of the lens system so that the aperture stop can be controlled by a relatively simple mechanism. The prior art has recognized that it is difficult to effectively correct astigmatism and field curvature in the zonal area of the image if the field angle is desired to be increased to 60.degree..
Although numerous examples of prior art references indicate that this is a close art, there is still room for improvement in correcting abberations such as astigmatism, field curvature and coma in the zonal to marginal areas of the image.
Examples of relevant prior art can be found in U.S. Pat. No. 3,615,126 and U.S. Pat. No. 3,895,857. Additional tesser type objective lens systems having rear aperture stops are disclosed in Japanese Utility Model Publication No. 42-22354, Japanese Patent Publications Nos. 50-3163 and 51-10092 and Japanese Patent Application Laid-Open to Public Inspection No. 49-38620.